Originally Posted by Dahon.Steve
You should never mountain bike with a 20 inch wheel which is why Dahon never made one that size. It's too dangerous and uncomfortable for mountain biking. I have a 20 inch wheel bike and it's less comfortable than a 26' or 27' inch tire by far. Furthermore, the smaller tires slips into cracks and pot holes which makes riding more dangerous at night or even during the day. Trust me.. I have a battle scars from falling off my folding bikes. Last, the smaller tire (especially the rear wheel) wears out faster than a 700 cc tire.
The 20' inch wheel is far from perfect.
I gave my eight year old nephew a nice BMX bike with HUGE tires on wide 20 inch rims. He doesn't like "to share", but I take it for short rides. The seatpost and stem work for him, and not for me. But the wheels and tires could go anywhere, anytime, with any rider.
I have waaay too many bike with umpteen gears and 26 inch and 27 inch tires. I envy my nephew's joy in riding his one speed BMX bike with those "go anywhere" wheels and tires. His bike can take anything an eight year old boy can imagine (and they can imagine doing stuff that gives adults nightmares). Some of my road bike wheels could go "out of true" if I just THINK about the stuff BMX riders get away with.